Koa Beck, sitting for 3-year-old Caleb in Brooklyn, says one mom paid her $20 an hour to watch her toddlers, and speak only French to them.Jonathan Baskin

With her lively personality, top-notch references and refined English accent, the prospective baby sitter appears to check all the boxes as a modern-day Mary Poppins.

She speaks about her passion for kids with the enthusiasm of a pageant queen holding out for world peace.

But the 20-something doesn’t come cheap.

“I charge $25 per hour,” she tells the West Village mom as the interview reaches its conclusion.

Then, the aspiring actress leans back in her seat and crosses her arms. The fee is not negotiable.

The attractive young woman is typical of New York City’s new breed of “super sitters” — bright young professionals who have first-aid training, a college degree and the word for diaper in four different languages.

Such is the demand, rates of $20 to $25 per hour are becoming the norm. If you want to keep the sitters sweet — and, more importantly, stop them from being spirited elsewhere — consider throwing in a tray of sushi, a generous tip and car service home.

“It is getting a little ridiculous,” says Claire, the mother of two who met with the super sitter after reading her references on an online parents’ group notice board. Asking The Post not to reveal her last name in case it deters future sitters, she adds: “When a date night with your husband costs $125 on top of your restaurant meal or movie tickets, you really have to think twice about going out.”

Over in Park Slope, mom of two Michelle Kaye, 35, feels the same pinch. “We pay between $15 and $17 per hour, and it starts to add up,” she says. “Handing over $90, plus the cost of a cab, pushes an already expensive night out right over the top.”

Gone is the day when the perky high school student down the block would happily watch your kids for $30 bucks and a can of Coke.

Earlier this year, research published by the Brooklyn-based support group Park Slope Parents found that 17 percent of baby sitters working for parents surveyed in the neighborhood were 21 or younger. By contrast, 57 percent were between the ages of 22 and 30.

“Teens are much busier now than they were 30 years ago,” says PSP founder Susan Fox. “College applications assume that you have other activities than schoolwork — and baby-sitting doesn’t count as an extra-curricular activity.”

That’s good news for the super sitters, the child caregiver/tutor hybrid who is particularly popular with families in tony Park Slope, TriBeCa and the Upper East Side. Many are background-checked and take credit cards though the new Web site UrbanSitter, the baby-sitting equivalent of OpenTable.

After all, in this tough economic climate, if you’re a college graduate struggling to find steady work in music, media, theater or p.r., earning $17 to $25 per hour (more than three times the minimum wage) as a baby sitter is an attractive option.

Take violinist Natalia Steinbach, 27, of Roosevelt Island, who has a bachelor’s degree from the prestigious Oberlin Conservatory of Music and more than 10 years of teaching experience.

She makes $60 per hour offering violin and viola lessons but regularly supplements her income baby-sitting at $20 an hour for one child. The fluent Russian speaker, who has nine top-rated references on UrbanSitter, says she only turns work down if it clashes with one of her concert performances.

“I have a knack for making kids smile, and they seem to like me because I treat them as friends and don’t talk down to them,” she says.

Then there’s Serena Brook, an actress living in Astoria, Queens, who enjoys veritable rock-star status on UrbanSitter.com with 18 repeat families, a “100 percent on-time” rating and at least 20 glowing references.

The former camp counselor writes in her online profile that she hopes to “not only look after and care for children while baby-sitting, but create a fun, stimulating environment.”

And there’s more. Specializing in children’s theater, she has appeared in off-Broadway shows such as “Dear Edwina” and “How the Grinch Stole Christmas.”

“I bring a lot to the table because I relate to kids easily,” says Brook, 26, who charges $17 per hour for one child, a minimum of $20 for two and $25 for three kids. “I love make-believe and all those weird imaginative games.”

Brook prefers to meet parents and kids ahead of any new baby-sitting job, so she gets to know the family’s needs beforehand. She also goes to regular face-to-face “meet-and-greet” sessions run by UrbanSitter that are designed to connect sitters with clients.

At the Web site’s recent baby-sitter/parent “speed-dating” event held inside a Park Slope wine bar, sitters were stationed at tables and got three minutes to impress prospective clients before the bell rang and the parent moved to the next candidate.

“I want to find someone who has experience with infants, is CPR-trained and is not going to sit around watching TV with them,” said new mom of one Carla Roberts, 33, a TV producer living in Windsor Terrace, who was there to vet baby-sitting candidates.

Spending hours with her charges in front of cartoons is a definite no-no for Brooklyn-based writer and editor Koa Beck, 25, a former super sitter who still picks up occasional gigs with school-age kids in Park Slope.

One mother hired her at $20 an hour to watch a pair of toddlers and speak only French to them. Another couple paid $300 for five hours of work helping to organize and chaperone at a birthday party.

Not one to blow her own trumpet, the editor-in-chief of the parent-oriented Web site Mommyish concedes that her confident banter, bachelor’s degree and experience traveling around Europe gel with the brownstone set.

“There must be a reason why strangers look at me and trust me with their children,” she says, wryly. “But I’ve never gotten a baby-sitting job without giving at least three references.

“The interview process is always more stressful [than other job interviews] because you not only have to impress the parents, but also the children.”

This being New York, affluent families can hire a professional to handle such interviews, conduct background checks, set rates and secure bookings.

Business is booming. Since its launch in September 2011, the number of sitters on Bell’s New York books has more than tripled, from 60 to 200. She has upward of 150 member families.

“All of my sitters are wholesome, dependable girls, mostly from the Midwest and Texas, who completed national criminal background checks, CPR- and first-aid training,” she explains. “They are smart, sophisticated and bring their own list of trophies to the table.”

Rates are set at $20 for one child, $22 for two and $25 for three kids, including a $5 per hour agency fee. It’s customary for parents to pay the sitter an added 20 percent tip.

Then there’s the small matter of what you place in the refrigerator for them to eat. The Girl Scout types employed by Lucky Lil’ Darlings wouldn’t dream of such presumption, but the odd super sitter can morph into a diva.

Sheryl Berk, an Upper East Side writer in her 40s and mom of one, is delighted with her daughter’s sitters, whom she pays an average of $20 an hour. Nevertheless, she has heard horror stories from friends who regularly face mandates for high-end sushi and sandwich deliveries.